1. Field of the Invention
The present invention relates to the technical field of dynamic random access memory (DRAM) management and, more particularly, to a memory use and management method and system for a multi-pass printer.
2. Description of Related Art
For a printer system at single-pass print, a printhead has to complete data print by single-pass, i.e., all required print positions are done. However, when the printhead requires successive printing for print dots at successive positions, the print dots may be distorted in shapes or sizes, and neighbor print dots may be out of focus due to short dried time so as to affect print quality.
To overcome the aforementioned problem, one solution applies multi-pass printing that printhead prints required data by several times. A printer can have modes of four-pass, eight-pass, etc. Multi-pass printing has advantages that shapes and sizes of successive print dots are not distorted in successive printing and neighbor print dots have longer dried time so as not to be out of focus and affect print quality. Thus, multi-pass printing can have better print quality.
However, multi-pass printing still has several defects. For example, for a four-pass mode, input data is divided into four times to print. In this case, if paper is fed in by a height of a printhead, required buffer is a size capable of storing data amount of two complete prints since printhead cannot be stopped to wait for next printing data to be completely filled up.
To overcome the problem in requiring a large buffer, U.S. Pat. No. 6,313,922 granted to Jackson, et al for an “Efficient use of a printhead and a compressed swath buffer in an inkjet printer” discloses a solution that a multi-pass printer can effectively use buffer to save memory use. If inkjet head of a printer has a height F as 100 (i.e., 100 inkjet holes) and four inkjet prints (four-pass, N=4), paper is fed in F/4 (25 inkjet holes) that is at a height of ¼ printhead. In this case, buffer is used as shown in FIGS. 1(A)–(D).
As shown in FIG. 1(A), 125 rows of data are stored in buffer. When inkjet head of a printer starts to move from right to left, upon first 25 rows of data (area indicated by A) as first pass, partial data in first 25 rows is used. As shown in FIG. 1(B), when paper for printing is fed in 25 rows and the inkjet head starts to move from right to left, upon first 25 rows of data as second pass, partial data in first 25 rows is used while upon 26 to 50 rows of data (area indicated by B) as first pass, partial data in 26 to 50 rows are used. Accordingly, the similarity is shown in FIGS. 1(C) and 1(D).
In FIG. 1(D), upon first 25 rows of data as fourth pass (the last one pass), first 25 rows of data are all used and thus discarded. In this case, 26 to 50 rows of data as third pass substitutes first 25 rows of data, 51 to 75 rows of data (area indicated by C) as second pass substitutes 26 to 50 rows of data, 76 to 100 rows of data (area indicated by D) as first pass substitutes 51 to 75 rows of data, and 101 to 125 rows of data substitutes 76 to 100 rows of data. However, if 101 to 125 rows of data cannot be filled up on time, inkjet head has to stop next swath printing until printing data is filled up.
In U.S. Pat. No. 6,313,922, each pass only prints partial data. In FIG. 1(A), because partial data in first 25 rows is used upon first 25 rows of data (area indicated by A) as first pass, masking is applied for determining which data is printed for use. FIG. 2 is a schematic diagram illustrating a multi-pass memory use and masking operation configured in U.S. Pat. No. 6,313,922. As shown, paper is fed in F/4 (25 inkjet holes) height after each print, i.e., going forward 1/N (N=4) swath in height, and thus use amount of memory is reduced to (1+1/N) swath of data amount, such that required buffer size is relatively reduced to 5/4 swath of data amount because only 1/N swath of data amount is required.
However, as cited, partial data in first 25 rows is used at first pass upon first 25 rows of data (area indicated by A) and stored in buffer until four passes are complete, and then discarded. Such a management wastes used buffer and is not optimized.
Therefore, it is desirable to provide an improved memory use and management method and system for a multi-pass printer to mitigate and/or obviate the aforementioned problems.